The present disclosure relates to a method of producing a coating solution with which glass used to produce solar collector modules is coated to enhance optical transmittance.
When the incident angle of light is vertical to glass, some of the incident light is lost through reflection at the air/glass interface. In this case, about 4% of the incident light is lost to reflection. For the glass used to cover a photovoltaic system, for example a photoelectric cell or a solar collector, the reflection loss decreases efficiency of the photovoltaic system. Therefore, a variety of methods have been attempted to produce a coating layer on the surface of glass in order to enhance light transmission through the glass.
When at least two layers of a high refractive index material and a low refractive index material are alternately stacked on each other, the wavelength of the reflected light disappears at a certain wavelength range. One example of such layers includes an anti-reflective layer formed on an architectural glass, such as glass from Schott Glaswerke. The anti-reflective layer is produced by the sol-gel method and is subjected to dip coating. The frequency bandwidth of such anti-reflective coatings is physically restricted to one octave, and the anti-reflective coatings are suitable only for visible light, not for the full solar spectrum, which has a wider bandwidth.
Korean Patent Publication No. 10-2008-0023888 describes anti-reflective glass for an automobile. The anti-reflective glass is designed to have low reflection by comprising a coating layer made of at least two materials of different refractive indices that absorb or optically interfere with visible light, thereby reducing the amount of reflected light. More particularly, a multilayer coating process has been attempted by stacking a number of layers through deposition. However, the multilayer coating is limited by the size of glass used for deposition, difficulty in mass-producing the film because film thickness must be controlled with high precision, and its low economical efficiency.
In order to solve these problems, a wet coating method has been proposed. For example, Korean Registered Patent No. 10-0653585 describes an anti-reflective film, a process for forming an anti-reflective film, and anti-reflective glass. The anti-reflective film containing fluorine atoms is produced by preparing a polysiloxane solution including fluoroalkylsilane and coating a film with the polysiloxane solution by using the conventional coating method. The wet coating method is impractical because fluoroalkylsilane is much more expensive than alkoxysilane, making it difficult to meet the price of the solar collector modules on the market.
Korean Registered Patent No. 10-0870213 describes a photocatalytic composition for anti-reflection and a glass substrate coated with the composition. Photocatalysts are proposed for anti-reflection and the production of an anti-reflective coating film using the photocatalysts, but the coating film has anti-reflective performance insufficient to improve solar cell efficiencies due to the intrinsic refractive index of titanium (Ti) used as the photocatalyst in the coating film.
Korean Patent Publication No. 10-2004-0035832 describes a hybrid sol for the production of abrasion-resistant SiO2 anti-reflection layers. Alkoxysilane is produced with a porous structure to produce an anti-reflective film. However, the alkoxysilane restricts storage stability of the coating solution under basic conditions, rendering it difficult to stably produce an anti-reflection coating film.